E34 # Is the Milky Way Unique?

The Basics

It is just one of billions of galaxies, but the Milky Way is our galaxy, our home in the universe.

Our first observations of stars, beginning with the naked eye and then with successively more powerful telescopes, happened here, providing a baseline for all the discoveries—and new questions—to follow.

One major question astronomers investigate when studying galaxies is how stars form within them. The James Webb Space Telescope’s powerful infrared instruments will improve our understanding of all stages of the star “lifecycle”—from birth to death and back again, to the rise of the next stellar generation. Astronomers know that stars form out of collapsing clouds of gas and dust, but they don’t yet know the exact sequence of how stars are born. What triggers a gas cloud to collapse? How much of that “mother” cloud does a star use up when it forms? How and when do planets begin to form around a new star?

At the end of their so-called lifecycle, stars “die” in a variety of dramatic and scientifically interesting ways—from gentle exhales of material to violent supernova explosions that expel stellar shrapnel into the galaxy. Many dying stars and stellar corpses are embedded in their ejected material; this shrouds them from view in visible light, but Webb’s infrared vision penetrates the dusty haze. Webb will help us probe and understand both this residual material and the former star. It allows astronomers to test their theories for how stars burn out, and how the heavier elements forged within these stars are recycled into the galactic environment to help create the next generation of stars.

Counting Stars

Webb will help us get a better grip on how many stars there are in the Milky Way and how those stars are distributed throughout the galaxy. The most common stars in the Milky Way are “dwarf stars” that are too dim for the Hubble Space Telescope to observe well in visible light, but that are easily visible in the infrared wavelengths that Webb can detect. Knowing how many dwarf stars there are, as well as other types of stars, also tells us how quickly or efficiently stars formed at various stages in the galaxy’s history. This will give astronomers a much more informed local baseline from which to compare and contrast other galaxies.

Credit: NASA/STScI